The beverage preparation apparatuses of the coffee machine type which use prepacked or non-packed portions of a food substance are very widespread among private individuals, and also in municipalities, shopping centres and companies. The preparation principle is based on the extraction of portions of the substance by the passage through this substance of a quantity of cold or hot liquid under high pressure, typically a pressure above atmospheric pressure. The prepacked portions can be partially rigid capsules, or else flexible bags, which are hermetically sealed or partially open, or else a dose filter.
An example of a capsule is described in patent EP 0 512 468 B1. An example of a bag is described in patent EP 0 602 203 B1.
Such extraction systems have many advantages. On the one hand, the individual packages are easy to use and require no batching of coffee or other substances, in the machine. The user places a capsule, a ground-coffee dose or other portions in the machine, then presses a button to start extraction. On the other hand, the individual packages are batched to deliver a beverage, like a coffee, having the desired characteristics such as sufficient character, flavour, foam or other important attributes. When they are impermeable, they usually preserve the freshness of the substance better, up to the time of extraction. Finally, the preparation conditions, such as the temperature, pressure and extraction time can be better controlled, thereby guaranteeing relatively controlled and constant quality to the consumer.
An example of an extraction method is described in EP 0 512 470 B1.
To extract a beverage under pressure from these portions, of the capsule or other type, it is necessary to use a relatively powerful water pump such as an electric compressor and electric heating elements that require significant amounts of electric power to heat water to the appropriate temperature for preparing hot beverages. These pumps and heating elements are usually supplied with electric energy from the mains.
It is therefore difficult to move these preparation apparatuses, for example on a trolley or simply by carrying them. In fact, it would be an advantage to be able to make these apparatuses more mobile so as to offer beverages in locomotion means such as the train, plane, or in certain places such as cinemas, theatres, and also in public places such as beaches, parks, poolsides and other public or private places.
U.S. Pat. No. 6,739,241 discloses a camping drip coffee maker in which a water is promoted from a reservoir to a brewing basket via a tube by heating the tube with an open flame heater to cause pressurisation of the water therein, whereby the boiling/evaporating water is promoted to the brewing basket. Whereas this type of flame heating of the water may prove to be convenient to circulate boiling/evaporated water under the effect of pressure for the purpose of making drip coffee, this heating system is not appropriate to be adapted to prepare an espresso. Indeed, the water which is pumped, usually mechanically, under pressure through ground coffee to prepare an espresso coffee is preferably maintained at a controlled temperature, typically at a temperature within a range of a few degrees around 85° C.
WO2006/102980 discloses an espresso machine that can be operated to prepare beverages without being connected to an electric power network. The machine is powered with a battery. To avoid extensive use of the battery to heat water used for the preparation of the beverages, the espresso machine has a thermally-insulated reservoir containing water that is preheated using the mains prior to prepare beverages in an autonomous mode. The water is then maintained at a sufficient temperature using the battery in the autonomous mode. The autonomy of such beverage machines can be of a few hours and thus provides a solution when their use is intended within a relatively short period from the time after the water has been preheated, for instance in trains, planes, cinemas . . . . However, this machine is not optimal when intended to be used only several hours or days after preheating the water.
US2007/0199452 discloses a mobile or portable espresso machine in which water is pumped from a reservoir by means of a pressure gas actuated pump. The water is heated in the reservoir (in which case the reservoir is insulated) or between the reservoir and the machine's extraction head. The espresso machine has either an electric heater, such as a thermoblock, or a combustion heater such as a burner using solid and/or gaseous and/or liquid fuel.
More generally, a fuel gas burner that may be used for cooking is disclosed in WO 2007/027379.
Even though combustion heaters may constitute an interesting alternative to electric heating for certain type of mobile or portable coffee machines, the known use of a combustion heater leads to boiling and/or evaporation of the water, which is not desirable for the preparation of espresso-type coffee or even tea. Moreover, such combustion heaters are sometimes not well accepted when the coffee machine is also intended to be used at proximity of the electric power supply, in particular at home.
Therefore, there is still a need to provide a handy mobile or portable espresso-type beverage machine that can be used to prepare beverages at home, in an office or even in the absence of an electric power network (mains) and which is suitable to prepare hot beverages from a liquid heated at a controlled temperature.